Emulsion explosives are well-known in the art; see, for example, U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,767; and 3,161,551. Emulsion explosives cartridges also are well-known from U.S. Pat. Nos. 4,790,890 and 4,867,920. Emulsions generally are formed at elevated temperatures, as required to keep the oxidizer salt(s) in solution. It has been found, however, that once the emulsion explosive is formed at the elevated temperature, it should be cooled rapidly to ambient temperature in order to preserve its long-term storage stability. Moreover, where such emulsion explosives are chemically gassed for sensitivity purposes, the formulated emulsion should be cooled quickly to minimize shrinkage or potential coalescence of the chemically generated gas bubbles within the emulsion. Accordingly, in forming chemically gassed, emulsion explosives cartridges, it is desirable to cool each cartridge as quickly as possible.
Packaged explosives or cartridges have been manufactured for many years. For example, dynamites have been paper-wrapped in conventional machines to form symmetrical cylindrical cartridges having crimped or "squared" ends that form planer surfaces perpendicular to the axis of the cylindrical cartridge. Packages in this form are convenient for handling, and when loaded into boreholes, have good end-to-end contact which facilitates cartridge-to-cartridge propagation upon detonation. The rigidity of the paper cartridge is advantageous for handling in certain applications.
Aqueous slurry explosives, which comprise a thickened gel of oxidizer salt solution throughout which a fuel is dispersed or dissolved, primarily have been packaged in a sausage-like form in a flexible tubing such as polyethylene having clipped ends. A process and apparatus for packaging slurry explosives in a sausage-like form is described in U.S. Pat. No. 3,783,735. The clipped ends, however, tend to interfere with close end-to-end contact, and thus clipped polyethylene tubes are not as desirable in certain applications as crimped paper tubes in assuring reliable detonation propagation from stick to stick in a loaded borehole. The handling characteristics of a flexible tube also may not be as desirable in some applications as that of paper cartridges.
More recently, emulsion explosives have been packaged either in crimped paper tubes, similar to that used for packaging dynamite, or in sausage-like clipped tubes, similar to that used for packaging slurry explosives. For certain applications and for the reasons set forth above, it is desirable to package emulsion explosives in symmetrical paper-wrapped cylinders having squared ends formed by crimping or other means. U.S. Pat. No. 4,790,890 discloses a method of manufacturing a chemically gassed emulsion explosives cartridge by first forming a cartridge of emulsion in flexible tubing and then over-wrapping the tube with an additional packaging material such as paper. This method has the disadvantage of requiring two separate packaging steps and materials with their attendant costs. U.S. Pat. No. 4,867,920 discloses another method for packaging chemically gassed emulsion cartridges with paper packaging. In this method, a chemically gassed slab of emulsion is immersed in water for cooling and then is cut into separate strips that then can be individually wrapped with paper. This requires, however, considerable handling of individual cartridges. The present invention overcomes these problems by providing a method for forming a paper-wrapped emulsion explosives cartridge in a continuous manner. The present invention allows for the cartridge to be cooled, such as by immersion in a water bath, after it has been paper-wrapped, and this method of "paper-wrapping into water" is precisely what the above-referenced prior art was trying to avoid, since heretofore it was not possible to paper-wrap a gassed cartridge and then subject it to water cooling because the paper or the adhesive or both were not compatible with water.
Emulsion explosives generally require some form of uniform distribution of gas bubbles for adequate detonation sensitivity. A common method of introducing sensitizing gas bubbles is incorporating a uniform distribution of void containing materials, such as glass or organic microspheres or perlite, throughout the emulsion. These void-containing materials tend not to migrate or coalesce once dispersed throughout the emulsion, and therefore, packaging of emulsions containing these materials is relatively simple.
Another means of sensitizing emulsion explosives is by the introduction of ingredients which react chemically to produce gas bubbles. Chemical gassing is a less expensive means of sensitization than the use of hollow microspheres and is therefore preferred from a cost standpoint. These free, discrete gas bubbles tend to migrate and/or coalesce in the emulsion or escape from the emulsion, however, unless inhibited by the viscosity of the emulsion itself. Because emulsions are relatively fluid at their elevated temperatures, it is important to cool them quickly and render them sufficiently viscous to minimize these problems. The invention allows for chemically gassed emulsion explosives to be paper-wrapped and then quickly cooled, a combination heretofore not available.